A surface light source device has been known in which a plurality of light emitting diodes (LEDs) is arranged in a matrix manner. The surface light source device is used as, for example, illumination means (back light) of a liquid crystal display device, and illuminates a liquid crystal display panel from its back-surface side in a planar manner.
In such a surface light source device (direct type in which LEDs are arrayed on the back-surface side of a liquid crystal display panel), a technique of local dimming (area-by-area light-adjustment control) has been known that improves contrast ratio between different divided areas in the same screen or reduces power consumption by separately controlling light intensity of the LEDs.
To perform local dimming control, techniques have been proposed for controlling light distribution of an LED by using a light flux controlling member having a rectangular shape (rectangular lens), or for adjusting luminance unevenness by arranging in the front side of an LED a reflection sheet (flatter) in which a plurality of small holes is provided.
As a surface light source device that enables local dimming control, an illuminator capable of illuminating a desired portion of a translucent light diffusion sheet with a clear outline has been proposed (e.g., see Patent Literature 1). The illuminator described in Patent Literature 1 is used in a liquid crystal display device, an illumination device and the like, includes a light reflecting member, a translucent light diffusion sheet, and light sources, and is supposed to be able to suppress interference of light emitted from the light sources arranged in respective recesses adjacent to each other on the light reflecting member.
As a surface light source device, an illumination device has also been known that reflects light from a light source by a concave mirror to irradiate a liquid crystal display panel with the light (e.g., see Patent Literature 2). According to the illumination device described in Patent Literature 2, it is supposed that independent luminance control for each divided area is possible, and that the shape of the light flux can be made to be a substantially square shape similar to the shape of the divided areas.